Setting a rating scale for assess rhizoctonia solani lesions on cotton, soybean and common bean seedlings

Abstract

Diseases incited by soilborne fungi are responsible for reducing the yield and cause significant impact to almost all crops. Among then, Rhizoctonia solani AG-4 is considered the most important in the cotton, common bean and soybean crops in Brazil. The use of diagrammatic scale or rating scales, as a tool to help in the quantification of the severity of a particular disease, is more common for foliar diseases. Considering the lack of a standardized, illustrated and easy-to-apply methodology for assessing the severity of R. solani lesions in cotton, soybean and common bean seedlings, a simple and precise rating scale was developed with the objective to fill this gap. The proposed scale shows four levels of disease severity, with the descriptions and illustrations for each type of lesion observed in the cotton, soybean and common bean seedlings. This developed scale was validated in many experiments and proved to be adequate for severity assessments of R. solani lesions on cotton, soybean and common bean seedlings.